Detection of counterfeit notes is currently a major concern. The counterfeiting of notes has become a perpetual problem not only in the United States but in many other countries. For example, Russia claims to be the second largest holder of U.S. currency in the world after the U.S.; however, it is recognized that much of this Russian-held U.S. currency is counterfeit.
Professionally made counterfeit notes are almost indistinguishable from valid notes and are extremely hard to detect even when very sophisticated detection equipment is employed. Thus, the challenge to governments and commerce directly affected by counterfeit notes are frequent and significant, particularly because counterfeiters and forgers always attempt to stay one step in advance of the latest counterfeit detection equipment.
Devices and methods for detecting counterfeit notes are the subject of several U.S. patents. A representative system is described in U.S. Pat. No. 5,491,325 to Huang et al. It discloses a method and system for payment and payment verification, including the steps of determining an index code which uniquely identifies the payment document and serves as an index into a data file; generating the data file using at least payment information associated with the payment document; imprinting the index code on the payment document; communicating the data file to a verification system; reading the index code from the payment document at the verification location; and verifying the authenticity of the payment document by accessing the data file and determining whether the read index code correctly identifies the payment document as an authorized payment document. The present invention is believed to provide significant advantages over this prior technology.